Salt debate raises blood pressure

Cutting too much salt from your diet may in some cases do more harm than good, an Australian researcher has warned.

Priscilla Kincaid-Smith, Emeritus Professor in Melbourne University's Department of Pathology says salt has both positive and negative effects in the body, and cautions against condemning it outright.

These claims by Professor Kincaid-Smith and colleague Professor Michael Alderman from the Albert Einstein College of Medicine in New York, appear in a lively debate over dietary sodium in the current edition of the Australian Medical Journal (MJA 1999; 170: 174-175).

She said that while it is well known that blood pressure falls when salt intake is reduced, this can also impact on several other important systems. For example, if salt intake is decreased, the levels of angiotensin II, a hormone known to be associated with heart attacks, can actually increase.

Professor Kincaid-Smith said some research suggests that high blood pressure alone is not responsible for vascular damage, because some patients with high blood pressure show little vascular damage, while others have a lot. Angiotensin II levels may be an additional culprit.

Other studies have found that reducing sodium intake, while lowering blood pressure, also increased blood levels of cholesterol and triglycerides, possibly with adverse effects. Blood levels of renin (which may have a role in heart disease) also increased.

"It is reasonable to consider the possibility that this effect (angiotensin II elevation) will swamp the potential benefit associated with the modest blood pressure fall produced by salt restriction," said Professor Kincaid-Smith.